Turbines are widely used in industrial and commercial operations. A typical commercial steam or gas turbine used to generate electrical power includes alternating stages of stationary vanes and rotating blades. The stationary vanes may be attached to a stationary component such as a casing that surrounds the turbine, and the rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as but not limited to steam, combustion gases, or air, flows through the turbine, and the stationary vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work.
Compressed working fluid that leaks around or bypasses the stationary vanes or rotating blades reduces the efficiency of the turbine. To reduce the amount of compressed working fluid that bypasses the rotating blades, the casing may include stationary shroud segments that surround each stage of rotating blades, and each rotating blade may include a tip shroud at an outer radial tip. Each tip shroud may include a seal rail that extends transversely across the tip shroud to form a seal between the rotating tip shroud and the stationary shroud segments. In addition, each tip shroud may include side surfaces that interlock with complementary side surfaces of adjacent tip shrouds to prevent adjacent tip shrouds from overlapping, reduce vibrations in the rotating blades, and enhance the seal between the rotating tip shrouds and the stationary shroud segments.
Over time, the side surfaces of the tip shrouds may erode or wear, creating gaps between adjacent tip shrouds that allow the rotating blades to twist and/or vibrate and increase the amount of compressed working fluid that bypasses the rotating blades. As a result, hardened materials are typically plated onto the side surfaces and periodically inspected to determine the amount of wear to the hardened materials. If the amount of wear is excessive, the entire rotating blade may need to be replaced. Otherwise, the tip shroud may be refurbished to restore and/or increase the thickness of the hardened materials on the side surfaces.
Previous efforts have been developed to determine the amount of erosion of the hardened materials. For example, measurements of various chord lengths across the tip shroud may be used to create a detailed coordinate map of the surface of the tip shroud. However, coordinate mapping is time-consuming and produces inconsistent results due to the geometric shape of the tip shroud. As a result, an improved apparatus and method for inspecting a turbine blade tip shroud would be useful.